Disposable dental tools are becoming more common due at least in part to increased awareness and concern for the spread of infectious diseases, such as hepatitis and AIDS. To remain cost-effective, disposable dental tools must be constructed of inexpensive plastics and manufactured in a relatively inexpensive manner so that they can discarded after use, thus eliminating the expense and inconvenience of sterilization.
Extrusion can produce dental tools and other parts having internal fluid passageways therein. But extrusion can only produce dental tools having a generally uniform cross-section or profile. Post-extrusion processing (e.g., machining, assembling, etc.) is required to add surface features, such as threads and ribs, to the extruded part.
Injection molding can also produce dental tools having internal fluid passages therein. With injection molding, a core pin within the mold cavity is surrounded by molding material that solidifies to form a passageway within the part. To withstand the relatively high pressures at which molding material is injected into the mold cavity, the core pin must have a sufficient moment of inertia relative to its length (e.g., be sufficiently rigid enough) to resist excessive flexing, deflection and/or deformation otherwise caused by the injection pressure.
Accordingly, it can be rather difficult, if not impossible, for existing injection molding systems to mold a part with a relatively small passageway in relation to the length of that passageway. This is because the required core pin would likely have too small of a moment of inertia relative to its length to resist excessive flexing, deflection and/or deformation caused by the injection pressure.